Method for making a sintered body having integral portions of different density

ABSTRACT

A method for forming a sintered body having integral porous, low density and non-porous, high density portions, comprising the steps of sintering and compacting a powder of a material selected from various metals, alloys, or cermets, in a form approximating a desired configuration, and compressing that portion only of the sintered compaction which is required to be of high density.

United States Patent Kimura et al.

METHOD FOR MAKING A SINTERED BODY HAVING INTEGRAL PORTIONS OF DIFFERENT DENSITY Inventors: Takashi Kimura; Yoji Awano, both of Nagoya, Japan Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho, Nagoya-shi, Aichi-ken, Japan Filed: July 21, 1972 Appl. No.: 273,946

Related US. Application Data Continuation of Ser. No. 4,352, Jan. 20, 1970, abandoned.

Foreign Application Priority Data Jan. 31, 1969 Japan 44-7607 US. Cl 29/182.2, 75/200, 75/208 R,

75/214, 142/107 M Int. Cl B22f 5/08 Field of Search 29/1822, 420.5; 75/200,

14 1 Apr. 9, 1974 Primary Examiner-Carl D. Quarforth Assistant Examiner-R. E. Schafer Attorney, Agent, or Firm-Herman, Bishoff & Platt [5 7] ABSTRACT A method for forming a sintered body having integral porous, low density and non-porous, high density portions, comprising the steps of sintering and compacting a powder of a material selected from various metals, alloys, or cermets, in a form approximating a desired configuration, and compressing that portion only of the sintered compaction which is required to be of high density.

4 Claims, 5 Drawing Figures WENTEDAPR 91m 3.802.849

FIG. 1

FIG. 2. 45

FIG. 3. I 55 INVENTORS.

ATTORNE Y3:

This is a continuation of application Ser. No. 4,352,

This invention relates to a method of forming a sintered compact body, such as a sintered alloy, having portions of different density by compressing separate portions of the body under different compression ratios.

Bodies formed of sintered materials are used for filters, oil-less bearings, and the like, because of their porosity, but they have disadvantages, such as low strength and low toughness, arising out of their high porosity.

Conventionally, when it has been desired to make and utilize products of high porosity and which also have great strength and toughness, it has been usual to provide reinforcement to the porous sintered material by backing the same with a material of high strength. However, such reinforcement complicates the manufacturing process, requiring numerous steps involving the added reinforcement materials and reinforcing treatment.

SUMMARY OF THE INVENTION The present invention relates to a method of forming a sintered compact body having portions with different properties and functions and which comprises the steps of sintering a metal, alloy, or cermet powder to form a body having approximately the shape and size of a desired product, and further compressing a portion of the body to higher density than that of the original porous sintered material, and thereby easily producing the product having integral low density, porous and high density, non-porous portions, wherein the high strength and toughness of the high density portion reinforces the weak, porous portion. Thus, the present method avoids the conventional complicated treatment such as backing with high strength material, or insertion into high strength parts. Such portion of the product as is required to be of high strength and toughness is subjected to compression at, or below the sintering temperature,

or at room temperature. The boundary between the porous portion and the high density portion of the product is naturally and continuously extended yielding strong, integral connection of the low and high density portions for reinforcement of the porous portion by the high density portion. The present invention yields a product having the advantages of simple processing, reduction of material costs by integral forming, and increase of production yield and efficiency.

It will be apparent from the above that the primary object of the present invention is to provide a method for forming a sintered product having portions of different density and which obviates the defects and disadvantages of conventional methods for forming such products.

Another object of the invention is to provide a method for simultaneously forming a sintered product having portions evidencing different physical characteristics and enabling versatile uses.

A further object of the invention is to provide a method for forming a sintered product which is easy to practice, and inexpensive and economical to follow.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the several figures, and in which:

FIG. 1 is a cross-sectional view of a mold apparatus used in the process according to the invention for forming the final product as a body of sintered material having portions of different density;

FIG. 2 is a cross-sectional view of a body formed of porous sintered material as initially formed prior to placement in the mold of FIG. 1;

FIG. 3 is a cross-sectional view of the final compacted product showing the body of FIG. 2 after it has been subjected to compression in the mold apparatus of FIG. 1;

FIG. 4 is a photomicrograph showing a cross-section of a portion of the product shown in FIG. 3; and

FIG. 5 is an enlarged photomicrographic view showing the integral boundary of the high and low density portions of FIG. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT The method of the present invention will be described as related to the forming of a synchronizer ring for use as a gear transmission part for automobiles.

Iron and carbon powders as a powder to be sintered are mixed in the proportion Fe-O.5%C and compacted in a die and sintered at l,l0OC. for 30 minutes to form the porous sintered ring 40 having a main ring body 41 with an inner peripheral surface 43, an outer peripheral surface 44, and an annular flange, or rim 42, having an upper surface 45 at an upper portion of the periphery of said ring body.

Another sample of the ring 40 was formed from Fe-2% Cu powder compacted in the die and sintered at 1,100C. for 15 minutes.

The rir n 42 of the porous sintered ring 40 was formed with a thickness larger than that of the corresponding rim of the product to be manufactured. The ring 40 was placed between die 10 and punch 20, FIG. 1, and further compressed at elevated temperature, thereby forming the product of desired configuration and dimensions and eliminating the pores in the rim 42 to obtain a rim of high density and reduced thickness. The elevated temperature used may be sintering temperature, or less, and may be reduced to room temperature.

The compression apparatus shown in FIG. 1 includes a metal die 10 and a punch 20, or ram, said die having an inner bottom surface 1 1, an inner cylindrical surface 12 directed vertically upwardly from the bottom surface, a stepped surface 13, or shoulder, directed outwardly from the surface 12 and having an appreciable inward, downward inclination, a side peripheral surface 14 directed upwardly vertically from the shoulder 13,

an upper end surface 15 directed outwardly at right angle to the surface 14, and a recess 19 in surface 15.

The punch 20 has a lower end surface 23, an outer FIG. 5 is an enlarged photomicrographic view of that portion of body 50 including the outer curved edge 57 between the main ring body 51 and the flange 52. This is the boundary between the porous ring 51 and the peripheral surface 22 directed upwardly with an out- 5 compressed, non-porous flange 52. As is apparent from ward inclination from the surface 23, and a ste ed the Figure, this boundary is not clearly, or sharply desurface 21, or shoulder, directed horizontally outfined, both p r i ng c nn y a fi rik dl f h Surface 22, A rdi l h h structure, which indicates that the porous and nonpunch 20 i i d i h meta] di to a i i porous portions are integrally connected in a continuin which the die shoulder contacts the punch shoul- 0115 and natural manner der 21, there remains a space 30 between the punch Sample rings formed of iron carbon y as P and die as shown in 1. In spaca 30, the distance ously noted, were made in the manner described above. between boundary walls defined by die surface 12 and The excess poymon 56 of h flange each rmg was the punch surface 22 is approximately the same as the cut m convenuor lal and R not thickness of the main ring body 41, 2. l5 shown, were machined on said flange portion 52 for gearing into the hub sleeve of an automobile transmission part, thus obtaining finished, or completed syn- In use of the compression apparatus, the punch is chmnizer rings T completed samplg l f rings were then each SUbJCCtd to an abrasion test, a 9 the 10 the mg heated a about 20 strength test, and a practical stroke abrasion test, the 900 C, IS inserted n the die so that theouter penpheral results of which am detailed below: Surface 44 of the 40 fangages Inner (he smfface In order to carry out the abrasion test in as practical The punch msened mm the meFal (he 10 a manner as possible, the inner peripheral surface 53 of Pnder compresswe force T the 40 f0rme d the synchronizer ring was periodically rubbed against h a Product p as sh own m l whlch has a mam 25 a tapered shaft under the following conditions; friction rmg body 51 an "melpenphera! Surface an speed 4.4m/sec.; friction load 15 kg; oil temperature Outer Surface and Surface 40-50c, load cycle 16 times/min. and load time 1.45 sec. a cycle, for 5,000 timesIThe wear was measured Durmg compmsslon by Punch 9 the mam rmg by the variation in the degree of insertion of the ta- 41 is only shghtly compressed at because (he pered shaft due to wear of the ring. The tapered shaft Space 30 has the Same dimensions as ring body was made of chrome steel havinga hardness of Hv 600. However, the flange 42 is compressed considerably Hardness vickers). since its thickness is greater than the corresponding In the Strength test, the load when the ring was p between the Shoulders 13 and Therefore tured by the insertion of the tapered shaft and the load main body 51 of product 50 retains about the same powhen all the teeth in the chamfeh or flangg, portion rosity as that of Portion 41 of the g but the were simultaneously bent and ruptured were measured: Pressed flange 52 has a much higher y- In other The stroke abrasion test was carried out by assembling wmds, resultant Product has a Porous PDrtioh 51 a sample synchronizer ring into an automobile transahd a hohpomus Portion, of high density Portion mission operating at 2,600 rpm of the propeller shaft; 40 the automobile gear was shifted between 4,280 rpm The temperature during Compression y Punch 20 and 2,600 rpm 32 times/min, for 50,000 times, and may preferably b about th temperature f r r ng, wear was measured by insertion of a tapered shaft into or somewhat lower, for materials which have high comthe disassembled ring, hereinbefore described. pressibility, while those materials having a smaller com- The following table shows the test results of the sampression ratio may be compressed at room temperaple synchronizerrings as compared with a conventional ture. synchronizer ring made by forging Fe-0.5%C steel:

Ring portion Flange portion Apparent Coetfi- Rupture Stroke ab- Apparent Rupture Sample density, Abrasion cient. of strength, rasion density, strength, Hardness, N0. Material g/cmi wear mm. friction ton wear mm. g./cm. ton HRB l FH.5% C sintered compact body. 6. 5 0. 10 O. 092 2. 3 0.03 7. 8 9.0 103 2 Fe-2% Cu sintered compact body. 6.6 0.20 0. 105 2.0 0.06 7. 8 6. 100 3 Foe-0.5% C conventionally forged material. 7.8 0.25 0. 085 2. 7 0.4 7.8 10.0 107 HRB: Hardness Rockwell Bee-ale.

The difference in density between portions 51,52 of the synchronizer ring will be apparent from the photomicrograph, FIG. 4, showing a cross-section of the ring obtained by sintering F e-0.5% C powder compact an? theFeaft'eniEnii-Essihg only "the rim porno? As is apparent from the table, the porous ring portion of Sample l has no appreciable difference in coefficient of friction as compared with Sample 3 obtained by conventionally forging the same material as Sample 1, while Sample 1 has remarkably less wear both in the abrasion test and stroke abrasion test. In the flange having high density, both samples have about the same strength and hardness. In comparing Sample 2 with conventional Sample 3 the results at ily slightly less favorable on the part of Sample 2 than Sample 1.

The synchronizer ring is required to have good wear resistance and a high coefficient of friction on the inner side of the ring portion, and the flange is required to have high strength for meshing with the inside gear of the transmission hub sleeve. It has been proved by the above tests and also by actual tests in cars that the sintered product of the present invention can be applied to parts which require high strength as has been indicated in the above table samples.

While the described synchronizer ring shows an example of the present invention in which the porous and high density portions are provided on opposite ends, it is possible to make a sintered product having said different portions disposed alternately. It is also possible to make a product having more than two portions which vary in density by suitably modifying the punch to exert different compressive forces in different areas.

In the described example of a synchronizing ring, compression was applied to the flange only, and weak, or no compression, such as not to change the porous characteristics, was applied to the main ring portion. For other products, the entire configuration and size, i.e., of all portions, may be modified simultaneously by the compression and molding step.

Although a certain specific embodiment of the invention has been shown and described, it is obvious that many modifications thereof are possible. The invention, therefore, is not intended to be restricted to the exact showing of the drawings and description thereof, but is considered to include reasonable and obvious equivalents.

We claim:

1. A method for producing a synchronizer ring, having a main ring body and outwardly directed teeth on the periphery of said ring body, comprising: the steps of compacting a powder to be sintered to form a green compact having a main ring body and an outwardly directed annular flange forming a rim at the upper portion of said body, both said rim and said body having substantially the same and uniform density;

sintering said compact; compressing said sintered compact in a die at about the sintering temperature of said compact or slightly lower by a single punch so constructed and arranged in relation to said die as to compress the rim more than the main ring body so as to form a fiber-like structure connecting the rim and body and to provide a compressed sintered compact whose density is higher in said outwardly directed rim than in the main ring body; and machining said rim to form outwardly directed teeth whereby said body and teeth are integrally formed of the same sintered material and connected to said ring body in a continuous and natural manner by said fiber-like structure, and said teeth have higher density than said main ring body.

2. A method for producing a synchronizer ring, according to claim 1, wherein said powder to be sintered is a ferrous metal powder selected from the group consisting of iron-carbon and iron-copper.

3. A synchronizer ring, comprising a main ring body and outwardly directed teeth at the upper portion of the periphery of said ring body, said body and teeth both being integrally formed of the same sintered material and connected in a continuous and natural manner by a fiber-like structure, and said teeth having higher density than said main ring body.

4. A synchronizer ring according to claim 3, wherein said sintered material is selected from the group consisting of iron-carbon alloy and iron-copper alloy. 

2. A method for producing a synchronizer ring, according to claim 1, wherein said powder to be sintered is a ferrous metal powder selected from the group consisting of iron-carbon and iron-copper.
 3. A synchronizer ring, comprising a main ring body and outwardly directed teeth at the upper portion of the periphery of said ring body, said body and teeth both being integrally formed of the same sintered material and connected in a continuous and natural manner by a fiber-like structure, and said teeth having higher density than said main ring body.
 4. A synchronizer ring according to claim 3, wherein said sintered material is selected from the group consisting of iron-carbon alloy and iron-copper alloy. 